1Z0-811 Java Basics and Syntax Practice Test 4 — 15 Questions

Question 1

Given: String s = "Java"; s.concat(" Rocks"); System.out.println(s); What prints?

Accepted Answer

"Java". Strings in Java are immutable. The `concat()` method returns a new string object but does not modify the original string `s`. Since the return value is not assigned to any variable, the original string `s` remains unchanged, so `System.out.println(s)` prints "Java".

Answer

"Rocks"

Answer

""

Answer

"Java Rocks"

Question 2

What is the result of: int[] arr = new int[5]; System.out.println(arr[5]);

Accepted Answer

ArrayIndexOutOfBoundsException. Java arrays are zero-indexed, meaning a valid index for an array of length 5 is 0 through 4. Accessing index 5 throws an ArrayIndexOutOfBoundsException at runtime, as it is outside the array's bounds.

Answer

null

Answer

-1

Answer

0

Question 3

Given: int day = 3; switch(day) { case 1: System.out.print("A"); case 2: System.out.print("B"); case 3: System.out.print("C"); case 4: System.out.print("D"); } What prints?

Accepted Answer

"CD". The switch statement does not have break statements, so after matching case 3, execution falls through to case 4, printing 'C' then 'D'. The output is 'CD'.

Answer

"BCD"

Answer

"C"

Answer

"ABCD"

Question 4

Given methods: void print(Integer i) { System.out.println("Integer"); } void print(int i) { System.out.println("int"); } What is output of print(10);?

Accepted Answer

"int". When calling print(10) with an integer literal, Java's method overloading resolution prefers the primitive int version over the Integer wrapper type because the literal 10 is a primitive int. The compiler selects the most specific matching method without requiring autoboxing, so the void print(int i) method is invoked, printing "int".

Answer

Compilation error

Answer

"Integer"

Answer

Runtime error

Question 5

Which assignment requires an explicit cast to compile?

Accepted Answer

int i = 10L;. Requires an explicit cast because it assigns a `long` literal (10L) to an `int` variable. In Java, `long` is a 64-bit type and `int` is 32-bit, so this is a narrowing primitive conversion that loses precision and must be explicitly cast with `(int)`. Without the cast, the compiler rejects it as a possible lossy conversion.

Answer

double d = 10;

Answer

long l = 10;

Answer

float f = 10.5f;

Question 6

Consider: for(int i=0;i<10;i++) { int x = i; } System.out.println(x); What is the result?

Accepted Answer

Compilation error. The variable `x` is declared inside the `for` loop block, so its scope is limited to that block. Attempting to use `x` outside the loop (in the `System.out.println(x);` statement) causes a compilation error because `x` is not in scope at that point. The Java compiler enforces block-level scoping rules, and any reference to a variable outside its declared block results in a 'cannot find symbol' error.

Answer

9

Answer

10

Answer

0

Question 7

Given method: static void change(String s) { s = "new"; } What is output of: String name = "original"; change(name); System.out.println(name);

Accepted Answer

"original". Java passes object references by value. Inside the method `change`, the local variable `s` is reassigned to a new String object, but this does not affect the original reference `name` in the main method. Strings are immutable, so the original `name` remains "original".

Answer

null

Answer

"new"

Answer

Compilation error

Question 8

What is the result of: Integer a = null; int b = (a != null) ? a : 0; System.out.println(b);

Accepted Answer

0. The ternary operator evaluates the condition (a != null). Since a is null, the condition is false, so the expression returns the second operand, which is the int literal 0. This value is assigned to int b, and System.out.println(b) prints 0. No NullPointerException occurs because the ternary operator never attempts to unbox a null reference.

Answer

NullPointerException

Answer

Compilation error

Answer

null

Question 9

Which TWO of the following are valid Java identifiers?

Accepted Answer

_count. (_count) is a valid Java identifier because identifiers can begin with an underscore (_) or a dollar sign ($), and can contain letters, digits, underscores, and dollar signs. Java allows underscores as the first character, though this is discouraged in modern Java style guides.

Answer

class

Answer

2ndValue

Answer

my-var

Question 10

Which TWO of the following are legal ways to declare and initialize an array?

Accepted Answer

int[] arr = new int[]{1,2,3};. It uses the valid syntax `int[] arr = new int[]{1,2,3};` which declares an array variable of type `int[]`, creates a new array object with an initializer list, and assigns it to the variable. This is a legal way to both declare and initialize an array in a single statement, as the array size is inferred from the number of elements in the initializer.

Answer

int arr = {1,2,3};

Answer

int arr[];

Answer

int[3] arr;

Question 11

Which THREE of the following are primitive data types in Java?

Accepted Answer

boolean. (boolean) is correct because boolean is one of the eight primitive data types in Java, representing a single bit of information with only two possible values: true or false. It is not an object and does not have methods, unlike reference types such as Boolean (the wrapper class).

Answer

void

Answer

String

Question 12

Refer to the exhibit. What is the likely cause of this error?

Accepted Answer

x is declared but not initialized. In Java, a local variable must be explicitly initialized before it is used; otherwise, the compiler reports an 'error: variable x might not have been initialized'. The exhibit shows a compilation error, and the most likely cause is that x was declared (e.g., 'int x;') but never assigned a value before being referenced in an expression or printed.

Answer

x is out of scope

Answer

x is a duplicate variable

Answer

x is declared as a different type

Question 13

Refer to the exhibit. What happens when you compile this code?

Accepted Answer

Compilation fails because num is final. The code fails to compile because the variable `num` is declared as `final`, meaning its value cannot be changed after initialization. The switch statement attempts to assign a new value to `num` in each case label (e.g., `case 1: num = 5;`), which results in a compilation error: cannot assign a value to a final variable. This is not a type mismatch; it is a violation of the final constraint.

Answer

Compilation fails because of type mismatch

Answer

Prints "Five"

Answer

Prints nothing

Question 14

Refer to the exhibit. What is the output?

Accepted Answer

12. The exhibit shows code that initializes an integer array with values 1 through 5. The enhanced for loop iterates over each element, adding each value to the variable 'sum' (starting at 0). After summing all five elements (1+2+3+4+5), sum equals 15. The code then prints the value of sum minus 3, which is 12. Therefore, option C is correct.

Answer

10

Answer

13

Answer

11

Question 15

A method is expected to receive an integer and return its square. Which method signature is correct?

Accepted Answer

int square(int x) { return x*x; }. The method signature specifies a return type of 'int' and includes the 'return' keyword to return the squared value. In Java, a method that returns a value must declare the return type before the method name and must use the 'return' statement to send the result back to the caller.

Answer

void square(int x) { return x*x; }

Answer

public square(int x) { return x*x; }

Answer

int square(int x) { x*x; }